/*
 * Copyright 2011 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.waveprotocol.box.webclient.client;

import com.google.gwt.dom.client.Element;

import org.waveprotocol.wave.client.scheduler.Scheduler;
import org.waveprotocol.wave.client.scheduler.SchedulerInstance;
import org.waveprotocol.wave.client.scheduler.TimerService;
import org.waveprotocol.wave.concurrencycontrol.common.UnsavedDataListener;

/**
 * Simple saved state indicator.
 *
 * @author danilatos@google.com (Daniel Danilatos)
 * @author yurize@apache.org (Yuri Zelikov)
 */
public class SavedStateIndicator implements UnsavedDataListener {

  private enum SavedState {
    SAVED("Saved"),
    UNSAVED("Unsaved...");

    final String message;

    private SavedState(String message) {
      this.message = message;
    }
  }

  private static final int UPDATE_DELAY_MS = 300;

  private final Scheduler.Task updateTask = new Scheduler.Task() {
    @Override
    public void execute() {
      updateDisplay();
    }
  };

  private final Element element;
  private final TimerService scheduler;

  private SavedState visibleSavedState = SavedState.SAVED;
  private SavedState currentSavedState = null;

  private static final String UNSAVED_HTML =
      "<span style='color: red; text-align: center;'>" + SavedState.UNSAVED.message
          + "</span>";
  private static final String SAVED_HTML =
      "<span style='color: green; text-align: center;'>" + SavedState.SAVED.message
          + "</span>";

  public SavedStateIndicator(Element element) {
    this.element = element;
    this.scheduler = SchedulerInstance.getLowPriorityTimer();
  }

  public void saved() {
    maybeUpdateDisplay();
  }

  public void unsaved() {
    maybeUpdateDisplay();
  }

  private void maybeUpdateDisplay() {
    if (needsUpdating()) {
      switch (currentSavedState) {
        case SAVED:
          scheduler.scheduleDelayed(updateTask, UPDATE_DELAY_MS);
          break;
        case UNSAVED:
          updateDisplay();
          break;
        default:
          throw new AssertionError("unknown " + currentSavedState);
      }
    } else {
      scheduler.cancel(updateTask);
    }
  }

  private boolean needsUpdating() {
    return visibleSavedState != currentSavedState;
  }

  private void updateDisplay() {
    visibleSavedState = currentSavedState;
    String innerHtml = visibleSavedState == SavedState.SAVED ? SAVED_HTML : UNSAVED_HTML;
    element.setInnerHTML(innerHtml);
  }

  @Override
  public void onUpdate(UnsavedDataInfo unsavedDataInfo) {
    if (unsavedDataInfo.estimateUnacknowledgedSize() != 0) {
      currentSavedState = SavedState.UNSAVED;
      unsaved();
    } else {
      currentSavedState = SavedState.SAVED;
      saved();
    }
  }

  @Override
  public void onClose(boolean everythingCommitted) {
    if (everythingCommitted) {
      saved();
    } else {
      unsaved();
    }
  }
}